1. Field of the Invention
The present invention relates to a power supply circuit of a mobile unit, and a mobile unit which moves by a non-contact power supply.
2. Description of the Related Art
Conventionally, a carriage system using a mobile unit (cart, etc.) having the function of carrying appliances, parts, etc. have been provided in the facilities of a factory, etc. The carriage system can typically be a mobile unit which has wheels and autonomously moves by a motor, etc. along rails fixed on the site. The system is not limited to this application. For example, it can be provided with a carriage cart lifted by magnetism, etc. In any case, with the configuration in which a mobile unit itself requires electric power, the conventional mobile unit is loaded with a battery.
However, it is necessary to load a large battery to operate such a mobile unit loaded with a battery continuously for a long time. In addition, the continuous operation is limited because the battery has to be periodically charged or replaced.
On the other hand, there is a method of supplying electric power to a mobile unit (cart) not by a loaded battery but by an induction line provided along the rails for a high frequency sine wave current, and high frequency power induced by a xe2x80x98coil having an iron corexe2x80x99 provided for the cart facing the induction line with a gap of several millimeters.
However, for example, when power is supplied by a plurality of high frequency power sources to a long distance rails or loop-shaped rails in this method, the induction line cannot be mounted without discontinuing the power supply. Therefore, power cannot be supplied to the cart running along the rails at some sections.
On the other hand, for example, Japanese Patent Publication No.8-98438 has suggested the following method. That is, with the configuration in which power is supplied through the above mentioned induction line, a cart is loaded with a cart battery 6 (lead storage battery) such that the battery can be charged while the cart is running, and the cart can continue running by the battery at the sections where the above mentioned induction line cannot supply electric power to the cart.
However, the method according to the above mentioned Japanese Patent Publication No.8-98438 has the following problems.
(1) Since the battery is limited in the number of repetitions of charge/discharge, it has to be periodically replaced (for example, every year or every second year).
(2) Since relatively a long time is required to charge the battery, the capacity of the battery is reduced when the cart frequently passes the no power supply sections.
(3) Since the battery is poor at a low temperature, it cannot be used outdoors or in a freezer.
(4) Since the battery has strong internal resistance, it cannot be quickly discharged, thereby failing in obtaining strong momentary power required to start or accelerate the cart.
(5) In the circuit according to Japanese Patent Publication No.8-98438, if the battery is in the discharged state, then electric power is supplied by high frequency induction first to charge the battery. Therefore, the cart cannot be immediately started.
The present invention aims at providing a power supply circuit capable of simultaneously supplying power to a driving device and charging a battery in a mobile unit to which power can be supplied without a contact, and allowing the mobile unit to move in any state without problems.
The power supply circuit according to the present invention is used for a mobile unit supplied with electric power through a power supply line mounted along the rails of the mobile unit without a contact. The circuit includes a chargeable/dischargeable battery, and a power supply/charge/discharge circuit for supplying the power obtained without a contact to the driving device and simultaneously distributing a part of the power to charge the battery when the power is supplied through the power supply line, and supplying the power from the battery to the driving device when the power is not supplied through the power supply line.
Using a charge/discharge battery, the power supply circuit with the above mentioned configuration can operate the mobile unit using the battery even at the sections having no power supply lines (no power supply sections). Furthermore, the circuit charges the battery at a section where a power supply line is provided, but with only a part of the supplied power used to charge the battery, thereby preventing the charging current from excessively flowing to the battery (that is, stopping the mobile unit) to incur the shortage of power to be provided for the driving device.
For example, by providing a limiting resistance for limiting the charging current to the battery, the mobile unit can keep (start) its operation although the battery is almost vacant (completely discharged).
Furthermore, if a DC-DC converter is provided at a stage subsequent to the supply/charge/discharge circuit, the value of the limiting resistance can be set such that it cannot be lower than the minimum input voltage of the DCDC converter by applying a voltage to both ends of the limiting resistance regardless of the state of the battery.
Thus, by setting an appropriate resistance value of the limiting resistance, the lower limit of the input voltage of the DC-DC converter can be maintained although the battery becomes almost vacant (completely discharged) and the voltage exceedingly drops, thereby suppressing any problems when electric power is supplied to the driving device through the DC-DC converter.
Furthermore, for example, since the battery can be quickly charged by using an electric double layer capacitor as the battery, the following effects can be obtained.
There are no problems occurring when a mobile unit frequently passes a no power supply section.
Since a battery can be quickly discharged, strong momentary power required to start or accelerate can be obtained.
A large capacity enables a cart to move without a power supply for a relatively long time
The present invention can also be configured as a mobile unit provided with the above mentioned power supply circuit.